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I've saved my progress as My aligned offspring.psd. In this exercise, we're going to make a couple of attempts at automatically blending these two images together. And it's not so much because I think there is any chance that we're going to achieve some kind of success here - in fact, the Auto-Blend command is going to fail spectacularly once again - however, it does give us the chance to see, when using the command, the difference between automatically correcting the exposure and colors of an image and leaving that check box off. So I'm going to turn off the GD off group here, and I'm going to click on the GD on group, and turn it on.
So we're going to apply the first blend to the background images here. I'll go up to the Edit menu, and I'll choose Auto-Blend Layers. Again, Photoshop is smart enough to know, because I have a group selected, I want it to blend all layers inside that group. I'll go ahead and choose Auto-Blend Layers, I'll make sure that Stack Images is selected, and I'll turn on Seamless Tones and Colors, as is turned on by default, by the way. Then I'll click OK in order to apply that modification. This time around what Photoshop is going to do is create this kind of ghosting effect between the boys because, again, it's not really designed to accommodate moving subjects like this, Auto-Blend Layers isn't.
It's assuming that everything is aligned before you apply it. However, what's interesting about this, and the reason that I'm demonstrating it to you is we do have these hard-edged masks. Once again, I'll Alt+Click or Option+Click on either one of these layer masks, and you'll see that we have very jagged transitions. So either a pixel is turned on or it's turned off - nothing in between and yet, if I Alt+Click or Option+Click again to bring back the full color composite image, we see this ghosting effect. In fact, notice that Sam's face is, this sort of duplicate of the right side of his face, notice that it has a pretty obvious edge up to a point, and then it just drops off.
It doesn't totally disappear; it drops away. The reason that's happening - let me show you this - I'm going to Shift+Click on the layer mask for a moment to turn it off so that we can see what has happened to the Sam layer. Photoshop has obviously corrected this area that was formerly inside of the mask. Notice if I Shift+Click on that layer mask thumbnail again, that was the area that was capped. I'll Shift+Click the thumbnail to turn it off once again. Notice that Auto-Blend went ahead and added an edge; it went ahead and added this little bit of tapering color there on this top layer.
So it doesn't just correct the overall image; it's correcting the image on a pixel-by-pixel basis. So you can just imagine the amazing amount of math that's going on here, the computational intensity doesn't happen to be working for us yet. It will in the future, as I say. All right! Just for the sake of comparison, I'm going to go ahead and click on the GD off group, turn it on, so that we can see the results of the modification here. So, we'll apply, once again, Auto-Blend Layers to the other group, and we'll see how it fares if that Seamless Tones and Colors check box is turned off.
So go up to the Edit menu, choose Auto-Blend Layers. This time I'm going to turn the check box off, as I say. Leave it set to Stack Images. You definitely want that. Click OK in order to apply the command. It should go a little faster this time around. Now we can see that there are no transitional colors. The layer masks are a little bit different this time; however, they're pretty similar to the way they were before. If you look at the thumbnails, they have a similar composition to them, whereas the effect is quite different, because Photoshop is no longer drawing in those transitional pixels into the layers themselves; so the pixels are either turned on or off. And they tend to be turned on as you can see here, on and off in these big chunks.
If I go ahead and draw a marquee, and then press the arrow key, 1, 2, 3, 4, in 4-pixel at a time chunk, so it's actually drawing 16 pixel blocks into these layer masks. So it's amazing that it's ever able to produce an interestingly transitional effect like this one here, as we saw in the first example. Anyway, that's not working for us, of course. I just want you to get a sense of what's going on in the background where Auto-Blend Layers is concerned. In the next exercise, we will manually mask these two layers into place.
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